Lubricating oil composition for diesel engines

ABSTRACT

Lubricating oil composition for use in diesel engines which comprises, in the base oil, not more than 0.3% by mass of sulphated ash, from 0.01 to 0.2% by mass of nitrogen in succinimides, from 0.05 to 0.12% by mass of zinc in zinc dithiophosphates, from 0.02 to 0.3% by mass of nitrogen in amine-based anti-oxidants, and from 0.01 to 0.08% by mass of boron, which further has a total value of [(zinc amount in zinc dithiophosphates)×(nitrogen amount in succinimides)] and [(zinc amount in zinc dithiophosphates)×(nitrogen amount in amine-based anti-oxidants)] as regards the aforementioned of from 0.015 to 0.06, and which does not contain salicylate, phenate or sulphonate metallic detergents. The intention is to obtain a lubricating oil composition for use in diesel engines which does not contain a metallic detergent yet maintains excellent engine (piston) detergency while preventing DPF clogging, and which reduces valve-train wear.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a lubricating oil composition for dieselengines, and in particular relates to a lubricating oil composition fordiesel engines having excellent engine (piston) detergency while beingextra low ash despite not incorporating metallic detergents.

BACKGROUND OF THE INVENTION

A diesel particulate filter (hereafter DPF), which is regarded as aneffective way of cleaning the particulate matter (hereafter PM) in theexhaust gases of diesel engines, may be subject to clogging of thefilter because of metal constituents in the engine oil used. Forexample, it is known that the ash deriving from diesel engine oilsaccumulates in the DPF, and that this gives rise to a reduction in thePM cleaning efficiency and a reduction in the life of the DPF, so thatit is considered necessary to reduce the sulphated ash in the dieselengine oil, in other words to lower the ash content.

This has meant that engine oils, and diesel engine oils in particular,have had a history of changing because of changes in the fuel. Forexample, particulates, carbon monoxide and NOx emissions fromatmospheric pollution due to exhaust gases are now a problem, and inparticular the sulphur content in diesel oils has sharply decreased overthe past ten or more years, from not more than 500 ppm to not more than10 ppm. Because of these exhaust-gas countermeasures, it has come aboutthat a post-treatment device known as a DPF has been installed in dieselengines. But in order to prevent clogging of the DPFs, a need has arisenfor low-ash engine oils.

Also, in the case of the sulphur content, given that sulphuric acid isformed by combustion and that the sulphuric acid so formed has adeleterious effect on piston detergency and on wear, and given thatphosphorus in the engines oils is known to poison the exhaust gaspurification catalysts, it is now conceivable that a trend favouring lowash/low phosphorus/low sulphur, known as “low SAPS” engine oils isbecoming ever stronger.

In this move towards lower ash, which has a major effect on the requiredperformance of the aforementioned diesel engines oils, it is necessaryto reduce the blended amounts of additives which contain metals, such asmetallic detergents which impart engine detergency, and zincdialkylthiophosphates (ZnDTP), which impart anti-wear performance.

In order to prevent the aforementioned clogging of the DPF, a low ashengine oil composition that contains no metallic additives can beconsidered, but if the metallic component is simply reduced compared toengine oil compositions of the prior art, the result will be a reductionin important functions, namely engine detergency, anti-wear performanceand oxidative stability of the engine oil composition.

For example, Japanese Laid-open Patent 2007-254559 (Patent Reference 1)has as its objective a low-ash diesel engine oil composition, but thesulphated ash is still considerable at up to 0.6% by mass, and itfurther contains a metallic detergent, so that so long as it uses asmall amount of metallic detergent, the situation is that it iscontinuing the prior art even with the objective of a low-ash engineoil.

Also, Japanese Laid-open Patent 2006-176672 (Patent Reference 2) has asits objective a lubricating oil for internal combustion engines withsuperior oxidative stability because of a low-ash component. It attemptsto offer an increased viscosity and acid number in this low-ash oil, butit does not specially focus on piston detergency. Furthermore, thesulphated ash in the examples is extremely large, at 0.99 to 1.01% bymass.

This invention is intended to obtain a lubricating oil composition foruse in diesel engines such that excellent engine (piston) detergency ismaintained while clogging of the DPF is prevented and wear on valvetrains is reduced, even without the inclusion of a metallic detergent.

This invention, without the inclusion of a metallic detergent, maintainsexcellent engine piston detergency while preventing clogging of the DPFand wear on valve trains, by creating a balance between zincdithiophosphates, succinimides and amine-based anti-oxidants added tothe base oil.

SUMMARY OF THE INVENTION

According to the present invention there is provided a lubricating oilcomposition for use in diesel engines which comprises, in the base oil,not more than 0.3% by mass of sulphated ash, 0.01 to 0.2% by mass ofnitrogen in succinimides, 0.05 to 0.12% by mass of zinc in zincdithiophosphates, 0.02 to 0.3% by mass of nitrogen in amine-basedanti-oxidants, and 0.01 to 0.08% by mass of boron, which further has atotal value of [(zinc amount in zinc dithiophosphates)×(nitrogen amountin succinimides)] and [(zinc amount in zinc dithiophosphates)×(nitrogenamount in amine-based anti-oxidants)]as regards the aforementioned offrom 0.015 to 0.06, preferably 0.015 to 0.04 and more preferably 0.015to 0.04, and which does not contain salicylate, phenate or sulphonatemetallic detergents.

DETAILED DESCRIPTION OF THE INVENTION

What is meant herein by not containing metallic detergents is alubricating oil composition wherein the metal component deriving frommetallic detergents is not more than 0.01% by mass.

The aforementioned base oil is preferably one that is a base oil or abase oil mixture selected from Group II, Group III, Group IV and Group Vand where the sulphur component of the base oil is not more than 50 ppm.

In addition, this lubricating oil composition for use in diesel enginesis such that the TGF in JASO M336:1998 Detergency Test Procedure is notmore than 30%, and the cam nose wear in JASO M354:1998 Valve-train WearTest Procedure is not more than 95 μm.

With this invention it is possible to obtain a lubricating oilcomposition for use in diesel engines such that no metallic detergent isincluded and there is a low amount of ash, while at the same timeexcellent piston detergency of the engine is maintained, clogging of theDPF is prevented and wear on valve trains is reduced, so that there is areduction in the burden on the environment.

For the base oil used in the lubricating oil composition for dieselengines of the present invention it is possible in particular to use asappropriate mineral oils, synthetic oils and mixtures thereof asnormally used for lubricating oils. In particular, it is possible touse, singly or as mixtures, oils which belong to categories Group II,Group III, Group IV and Group V of the API (American PetroleumInstitute) base oil categories.

The aforementioned Group II base oils include, for example, paraffinicmineral oils obtained by appropriate use of a suitable combination ofrefining processes such as hydrocracking and dewaxing in respect oflubricating oil fractions obtained by atmospheric distillation of crudeoil. Group II base oils refined by hydrorefining methods such as theGulf Company method have a total sulphur content of less than 10 ppm andan aromatic content of not more than 5% and so can be used for thisinvention.

The viscosity of these base oils is not specially limited, but theviscosity index should be 80 to 120 and preferably 100 to 120. Thekinematic viscosity at 40° C. should preferably be 2 to 680 mm²/s andmore preferably 8 to 220 mm²/s. Also, the total sulphur content shouldbe less than 300 ppm, preferably less than 100 ppm and more preferablyless than 10 ppm. The total nitrogen content should also be less than 10ppm and preferably less than 1 ppm. In addition, oils with an anilinepoint of 80 to 150° C. and preferably 100 to 135° C. should be used.

Group 2 Plus base oils, which possess the viscosity index higher than115, can be specified as a preferable Group 2 base oil.

Group III base oils include, for example, paraffinic mineral oilsmanufactured by a high degree of hydrorefining in respect of lubricatingoil fractions obtained by atmospheric distillation of crude oil, baseoils refined by Isodewaxing which dewaxes and substitutes withisoparaffins waxes produced by dewaxing processes, and base oils refinedby the Mobil wax isomerisation process. These are also suitable for usein this invention.

The viscosity of these base oils is not specially limited, but theviscosity index should be 120 to 160 and preferably 120 to 150. Thekinematic viscosity at 40° C. should preferably be 2 to 680 mm²/s andmore preferably 8 to 220 mm²/s. Also, the total sulphur content shouldbe less than 300 ppm, preferably less than 100 ppm and more preferablyless than 10 ppm. The total nitrogen content should also be less than 10ppm and preferably less than 1 ppm. In addition, oils with an anilinepoint of 80 to 150° C. and preferably 110 to 135° C. should be used.

Group 3 Plus base oils, which possess the viscosity index higher than130, can be specified as a preferable Group 3 base oil.

As examples of synthetic oils, mention may be made of polyolefins,alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols,polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds(perfluoropolyethers, fluorinated polyolefins and so on), and silicones.

The aforementioned polyolefins include polymers of various olefins orhydrides thereof. Any olefin may be used, and as examples mention may bemade of ethylene, propylene, butene and α-olefins with five or morecarbons. In the manufacture of polyolefins, one kind of theaforementioned olefins may be used singly or two or more kinds may beused in combination. Particularly suitable are the polyolefins calledpoly-α-olefins (PAO). These are base oils of Group IV.

The viscosity of these synthetic oils is not specially limited, but thekinetic viscosity at 40° C. should preferably be 2 to 680 mm²/s and morepreferably 8 to 220 mm²/s.

GTLs (gas to liquid) synthesised by the Fischer-Tropsch method ofconverting natural gas to liquid fuel have a very low sulphur contentand aromatic content compared with mineral oil base oils refined fromcrude oil and have a very high paraffin constituent ratio, and so haveexcellent oxidative stability, and because they also have extremelysmall evaporation losses, they are suitable as base oils for thisinvention.

The viscosity characteristics of GTL base oils are not speciallylimited, but normally the viscosity index should be 120 to 180,preferably 130 to 175, and more preferably 140 to 175. Also, thekinematic viscosity at 40° C. should be 2 to 680 mm²/s and preferably 5to 120 mm²/s. Normally the total sulphur content is also less than 10ppm and the total nitrogen content less than 1 ppm. A commercial exampleof such a GTL base oil is Shell XHVI (registered trademark).

Base oils specified above can be used singly or as mixtures, and theirsulphur content should be less than 50 ppm, preferably less than 10 ppmand more preferably less than 1 ppm.

As examples of the aforementioned zinc dithiophosphates, mention may bemade in general of zinc dialkyl dithiophosphates, zinc diaryldithiophosphates and zinc arylalkyl dithiophosphates. For example, zincdialkyl dithiophosphates where the alkyl groups of the zinc dialkyldithiophosphates have primary or secondary alkyl groups of 3 to 22carbons or alkylaryl groups substituted with alkyl groups of 3 to 18carbons may be used. For example, zinc dialkyl dithiophosphates wherethe alkyl groups of the zinc dialkyl dithiophosphates have primary orsecondary alkyl groups of 3 to 12 carbons or zinc diaryldithiophosphates where the aryl groups are phenyl or alkylaryl groupssubstituted with alkyl groups of 1 to 18 carbons may be used.

The zinc dithiophosphates with secondary alkyl groups having 3 to 12carbon atoms, preferably 3 to 8 carbon atoms and more preferably 3 to 6atoms are preferred.

As specific examples of zinc diallyl dithiophosphates, mention may bemade of zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate,zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zincdiisopentyl dithiophosphate, zinc diethylhexyl dithiophosphate, zincdioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc didecyldithiophosphate, zinc didodecyl dithiophosphate, zinc dipropylphenyldithiophosphate, zinc dipentylphenyl dithiophosphate, zincdipropylmethylphenyl dithiophosphate, zinc dinonylphenyl dithiophosphateand zinc didodecylphenyl dithiophosphate.

These zinc dithiophosphates are incorporated so that the amount of zincis 0.05 to 0.12% by mass, but preferably 0.06 to 0.12% by mass, of thelubricating oil composition. Zinc dithiophosphates are, as mentionedabove, effective anti-wear additives, but they contain phosphorus (P).Phosphorus compounds are said to poison exhaust-gas catalysts, and ifthe phosphorus content in the composition increases, there is aheightened possibility of a deleterious effect on the exhaust-gascleaning catalyst. For this reason, if the zinc dithiophosphate isincorporated so that the amount of zinc exceeds 0.12% by mass, therewill be a concomitant increase in the amount of phosphorus in thecomposition, which is not desirable. Also, if the aforementioned upperlimit is exceeded, the effect of being a wear additive will besaturated, so that an effect matching the expenditure will not beobtained and this will not be efficient. On the other hand, if theamount is less than 0.05% by mass, the result in terms of being ananti-wear additive may not be effectual.

In the lubricating oil composition of this invention, an alkenylsuccinimide or an alkyl succinimide and/or a boron-modified derivativethereof is used for the aforementioned succinimide. It has the functionof being an ashless dispersant.

As suitable examples of an alkenyl or an alkyl succinimide mention maybe made of the alkenyl or alkyl succinic monoimides represented byGeneral Formula (1) and the alkenyl or alkylsuccinic bisimidesrepresented by General Formula (2).

In the aforementioned General Formula (1) and General Formula (2), R¹,R³ and R⁴ each denote an alkenyl group or an alkyl group with aweight-average molecular weight of from 500 to 3,000, and R³ and R⁴ maybe the same or different. R², R⁵ and R⁶ each denote an alkylene grouphaving from 2 to 5 carbons, and R⁵ and R⁶ may be the same or different.m is an integer of from 1 to 10 and n is 0 or an integer of from 1 to10.

The weight-average molecular weight of each of R¹, R³ and R⁴ in GeneralFormulae (1) and (2) is, as aforementioned, from 500 to 3,000, butpreferably from 1,000 to 3,000. If the weight-average molecular weightis less than 500, solubility in the base oil will be reduced, and if itexceeds 3,000 detergency will decrease, so that there will be a riskthat the target functions will not be achieved.

Also, the aforementioned m is an integer of from 1 to 10, but preferablyfrom 2 to 5, and more preferably from 3 to 4. If m exceeds 2, there willbe good detergency. If m is less than 5 solubility in the base oil willbe good.

In General Formula (2), n is 0 or an integer of from 1 to 10, butpreferably from 1 to 4 and more preferably from 2 to 3. If n exceeds 1,there will be good detergency, and if n is less than 4 solubility in thebase oil will be good.

As examples of the alkenyl groups in General Formulae (1) and (2),mention may be made of polybutenyl groups, polyisobutenyl groups, andethylene-propylene copolymers. Alkyl groups include hydrogenated formsthereof. As typical examples of suitable alkenyl groups mention may bemade of polybutenyl groups and polyisobutenyl groups. These polybutenylgroups are obtained by polymerising mixtures of 1-butene and isobuteneor highly refined isobutene.

Also, hydrogenated forms of polybutenyl groups or polyisobutenyl groupsare typical examples of suitable alkyl groups.

The aforementioned alkenyl or alkyl succinimides can normally beprepared by reacting with a polyamine an anhydrous alkenyl succinimideobtained by a reaction between a polyolefin and maleic anhydride, or ananhydrous alkyl succinimide obtained by hydrogenating same.

The aforementioned succinic monoimides and bisimides may be prepared byvarying the reaction proportions of anhydrous alkenyl succinic acids oranhydrous alkyl succinic acids and polyamines.

For the olefin monomer that forms the aforementioned polyolefin, it ispossible to use mixtures of one or two or more kinds of α-olefins havingfrom 2 to 8 carbons, and it is possible to use satisfactorily mixturesof isobutene and butene-1.

As examples of the aforementioned polyamines, mention may be made ofunitary diamines such as ethylene diamine, propylene diamine, butylenediamine and pentylene diamine, and of polyalkylene polyamines such asdiethylene triamine, triethylene tetramine, tetraethylene pentamine,pentaethylene hexamine, di(methylethylene) triamine, dibutylenetriamine, tributylene tetramine and pentapentylene hexamine.

Also, for boron-modified derivatives of alkenyl or alkyl succinimides itis possible to use those prepared by the usual methods. For example,they can be obtained after making the aforementioned polyolefins intoanhydrous alkenyl succinimides by reacting them with maleic acid, byfurther imidification through reacting them with an intermediateobtained by reacting the aforementioned polyamines and a boron compoundsuch as boron oxide, a boron halide, a boric acid, a boric anhydride, aboric ester or an ammonium salt of a boric acid.

The lubricating oil composition of this invention contains, in terms ofthe composition, from 0.01 to 0.2% by mass, calculated in terms ofnitrogen content, of an alkenyl or alkyl succinic monoimide or bisimideand/or a boron-modified derivative thereof as an ashless dispersant, butpreferably contains from 0.05 to 0.15% by mass.

If the content of the alkenyl or alkyl succinic monoimide or bisimideand/or boron-modified derivative thereof is less than 0.01% by mass, theeffect as an ashless dispersant will not be satisfactorily displayed,and if it exceeds 0.2% by mass, deleterious influence on rubber partssuch as elastomers used in engines can be seen.

Also, the content of a boron-modified derivative of an alkenyl or alkylsuccinic monoimide in said ashless dispersant will be, calculated interms of boron, from 0.01 to 0.08% by mass and preferably from 0.04 to0.07% by mass.

Even if the boron-converted content of the alkenyl or alkyl succinicmonoimide and/or boron-modified derivative thereof in the ashlessdispersant is less than 0.01% by mass the effect of the anti-wear andhigh temperature detergency performance is not enough and if it exceeds0.08% by mass, that effective performance will be saturated and theeconomic efficiency will decrease.

Also, boron derives from boron-modified forms of succinimides, and forthe amount of succinimide added to be within the aforementioned range,it is often not desirable if the boron component is added in excess,because the excess of the boron component may cause the DPF clogging byincreasing the sulphated ash derived by increased boron in theformulation.

For the amine-based anti-oxidants used in this invention, those usedgenerally for lubricating oils are preferred for practical use, and itis possible to use them singly or in plural combinations in thelubricating oil composition within the range of from 0.02 to 0.3% bymass in terms of the nitrogen content.

Amine-based anti-oxidants structurally are prone to surface adsorption,and because the zinc dithiophosphate, the anti-wear agent, decomposesand the acidic intermediates are adsorbed on the surface, an excessadded amount is again not desirable, so that it is best to control theupper limit.

As examples of the aforementioned amine-based anti-oxidants, mention maybe made of dialkyldiphenylamines such as p,p′-dioctyldiphenylamine(Nonflex OD-3, made by Seiko Chemical Ltd),p,p′-di-α-methylbenzyldiphenylamine andN-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such asmono-t-butyldiphenylamine and monooctyldiphenylamine,bis(dialkylphenyl)amines such as di(2,4-diethylphenyl)amine anddi(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such asoctylphenyl-1-naphthylamine and N-t-dodecylphenyl-1-naphthylamine,1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine,phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine andN-octylphenyl-2-naphthylamine, phenylenediamines such asN,N′-diisopropyl-p-phenylenediamine andN,N′-diphenyl-p-phenylenediamine, and phenothiazines such asPhenothiazine (made by Hodogaya Chemical Ltd.) and3,7-dioctylphenothiazine.

Apart from the amine-based anti-oxidants used in this invention, it ispossible to use phenolic anti-oxidants. In the undermentioned examples,phenolic anti-oxidants and amine-based anti-oxidants are used incombination. These anti-oxidants may be used singly or in pluralcombinations within the range of from 0.01 to 5% by mass in thelubricating oil composition.

The combination of the amine-based anti-oxidants and phenolicanti-oxidants used in the Examples shown in Table 1.

As examples of sulphur-based anti-oxidants, mention may be made ofdialkyl sulphides such as didodecyl sulphide, thiodipropionate esterssuch as dioctadecyl thiodipropionate, dimyristyl thiodipropionate anddodecyloctadecyl thiodipropionate, and 2-mercaptobenzoimidazole.

Phenolic anti-oxidants include 2-t-butylphenol,2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol,2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol,2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol,2,5-di-t-butylhydroquinone (Antage DBH, made by Kawaguchi ChemicalIndustry Co. Ltd.), 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-alkylphenolssuch as 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol,and 2,6-di-t-butyl-4-alkoxyphenols such as2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol.

Also, there are 3,5-di-t-butyl-4-hydroxybenzylmercapto-octylacetate,alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionates such asn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate (Yoshinox SS,made by Yoshitomi Fine Chemicals Ltd.),n-dodecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate and2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate,benzenepropanoic acid 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-C₇-C₉side-chain alkyl ester (Irganox L135, made by Ciba Specialty ChemicalsLtd.), 2,6-di-t-butyl-α-dimethylamino-p-cresol, and2,2′-methylenebis(4-alkyl-6-t-butylphenol)s such as2,2′-methylenebis(4-methyl-6-t-butylphenol) (Antage W-400, made byKawaguchi Chemical Industry Ltd.) and2,2′-methylenebis(4-ethyl-6-t-butylphenol) (Antage W-500, made byKawaguchi Chemical Industry Ltd).

Furthermore, there are bisphenols such as4,4′-butylidenebis(3-methyl-6-t-butylphenol) (Antage W-300, made byKawaguchi Chemical Industry Ltd.),4,4′-methylenebis(2,6-di-t-butylphenol) (Ionox 220AH, made by ShellJapan Ltd.), 4,4′-bis(2,6-di-t-butylphenol),2,2-(di-p-hydroxyphenyl)propane (Bisphenol A, made by Shell Japan Ltd.),2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane,4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethylene glycolbis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (Irganox L109, made byCiba Specialty Chemicals Ltd.), triethylene glycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] (Tominox 917, madeby Yoshitomi Fine Chemicals Ltd.),2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (IrganoxL115, made by Ciba Specialty Chemicals Ltd.),3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane(Sumilizer GA80, made by Sumitomo Chemicals),4,4′-thiobis(3-methyl-6-t-butylphenol) (Antage RC, made by KawaguchiChemical Industry Ltd.) and 2,2′-thiobis(4,6-di-t-butyl-resorcinol).

Mention may also be made of polyphenols such astetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]methane(Irganox L101, made by Ciba Specialty Chemicals Ltd.),1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Yoshinox 930, madeby Yoshitomi Fine Chemicals Ltd.),1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (Ionox330, made by Shell Japan Ltd.),bis-[3,3′-bis-(4′-hydroxy-3′-t-butylphenyl) butyric acid]glycol ester,2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and2,6,-bis(2′-hydroxy-3′-t-butyl-5′-methyl-benzyl)-4-methylphenol, andphenol-aldehyde condensates such as condensates of p-t-butylphenol andformaldehyde and condensates of p-t-butylphenol and acetaldehyde.

In addition to the aforementioned constituents, where required byapplications or performance, it is also possible to use as appropriatemetal deactivators, corrosion inhibitors, viscosity index improvers,pour point depressants, defoaming agents and other additives in thelubricating oil composition for diesel engines of this invention.

Metal deactivators that can be used together with the lubricating oilcomposition for diesel engines of this invention include benzotriazoleand benzotriazole derivatives which are 4-alkyl-benzotriazoles such as4-methyl-benzotriazole and 4-ethyl-benzotriazole, 5-alkyl-benzotriazolessuch as 5-methyl-benzotriazole and 5-ethyl-benzotriazole,1-alkyl-benzotriazoles such as 1-dioctylaminomethyl-2,3-benzotriazoleand 1-alkyl-tolutriazoles such as 1-dioctylaminomethyl-2,3-tolutriazole,and benzoimidazole and benzoimidazole derivatives which are2-(alkyldithio)-benzoimidazoles such as 2-(octyldithio)-benzoimidazole,2-(decyldithio)-benzoimidazole and 2-(dodecyldithio)-benzoimidazole and2-(alkyldithio)toluimidazoles such as 2-(octyldithio)-toluimidazole,2-(decyldithio)-toluimidazole, and 2-(dodecyldithio)toluimidazole.

Also, mention may be made of indazole, indazole derivatives which aretoluindazoles such as 4-alkyl-indazoles and 5-alkyl-indazoles,benzothiazole, and benzothiazole derivatives which are2-mercaptobenzothiazole derivatives (Thiolite B-3100, made by ChiyodaChemical Industries Ltd.), 2-(alkyldithio)benzothiazoles such as2-(hexyldithio)benzothiazole and 2-(octyldithio)benzothiazole,2-(alkyldithio)toluthiazoles such as 2-(hexyldithio)toluthiazole and2-(octyldithio)toluthiazole,2-(N,N-dialkylydithiocarbamyl)-benzothiazoles such as2-(N,N-diethyldithiocarbamyl)-benzothiazole,2-(N,N-dibutyldithiocarbamyl)-benzothiazole and2-(N,N-dihexyldithiocarbamyl)-benzothiazole, and2-(N,N-dialkyldithiocarbamyl)-toluthiazoles such as2-(N,N-diethyldithiocarbamyl)-toluthiazole,2-(N,N-dibutyldithiocarbamyl)-toluthiazole and2-(N,N-dihexyldithiocarbamyl)-toluthiazole.

Further, mention may be made of benzooxazole derivates which are2-(alkyldithio)benzooxazoles such as 2-(octyldithio)benzooxazole,2-(decyldithio)benzooxazole and 2-(dodecyldithio)benzooxazole or whichare 2-(alkyldithio)toluoxazoles such as 2-(octyldithio)toluoxazole,2-(decyldithio)toluoxazole and 2-(dodecyldithio)toluoxazole, thiadiazolederivatives which are 2,5-bis(alkyldithio)-1,3,4-thiadiazoles such as2,5-bis(heptyldithio)-1,3,4-thiadiazole,2,5-bis(nonyldithio)-1,3,4-thiadiazole,2,5-bis(dodecyldithio)-1,3,4-thiadiazole and2,5-bis(octadecyldithio)-1,3,4-thiadiazole,2,5-bis(N,N-dialkyldithiocarbamyl)-1,3,4-thiadiazoles such as2,5-bis(N,N-diethyldithiocarbamyl)-1,3,4-thiadiazole,2,5-bis(N,N-dibutyldithiocarbamyl)-1,3,4-thiadiazole and2,5-bis(N,N-dioctyldithiocarbamyl)-1,3,4-thiadiazole and2-N,N-dialkyldithiocarbamyl-5-mercapto-1,3,4-thiadiazoles such as2-N,N-dibutyldithiocarbamyl-5-mercapto-1,3,4-thiadiazole and2-N,N-dioctyldithiocarbamyl-5-mercapto-1,3,4-thiadiazole, and triazolederivates which are, for example, 1-alkyl-2,4-triazoles such as1-dioctylaminomethyl-2,4-triazole.

These metal deactivators may be used singly or in plural combinationswithin the range of from 0.01 to 0.5% by mass in the lubricating oilcomposition.

As examples of the aforementioned corrosion inhibitors, mention may bemade of fatty acids, alkenylsuccinic half-esters, fatty acid soaps,alkyl sulphonic acid salts, sulphonates, and naphthenates of alkalineearth metals (calcium (Ca), magnesium (Mg), barium (Ba) and so on),polyhydric alcohol fatty acid esters, fatty acid amines, paraffin oxide,and alkylpolyoxyethylene ethers, and normally the amount thereof in theblend will be within the range of from 0.01 to 5% by mass on the basisof the total amount of the composition.

In order to improve the low-temperature flow characteristics andviscosity characteristics, pour-point depressants and viscosity-indeximprovers can also be added to the lubricating oil composition of thisinvention.

As examples of viscosity-index improvers mention may be made ofnon-dispersant type viscosity-index improvers such as polymethacrylatesas well as ethylene-propylene copolymers, styrene-diene copolymers suchas styrene-butadiene or olefin polymers such as polyisobutylene andpolystyrene, and dispersant type viscosity-index improvers wherenitrogen-containing monomers have been copolymerised with these. Asregards the amount to be added, they may be used within the range offrom 0.05 to 20% by mass of the lubricating oil composition.

As examples of pour-point depressants mention may be made ofpolymethacrylate-based polymers. As regards the amount to be added, theymay be used within the range of from 0.01 to 5% by mass of thelubricating oil composition. A polymethacrylate-based pour-pointdepressant was incorporated in the examples of this invention.

Defoaming agents may also be added in order to impart defoamingcharacteristics to the lubricating oil composition of this invention. Asexamples of preferred defoaming agents, mention may be made oforganosilicates such as polydimethylsiloxane, diethylsilicate andfluorosilicone, and non-silicone type defoaming agents such aspolyalkylacrylates. As regards the amount to be added, they may be usedsingly or in plural combinations within the range of from 0.0001 to 0.1%by mass in the lubricating oil composition.

Further explanation is given below by giving examples and comparativeexamples, but the invention is not limited by these.

In preparing the examples and comparative examples, the followingcompositions and materials were used.

1. Base oils(1-1) Base Oil A: Fischer-Tropsch derived base oil (XHVI 5.2)[Characteristics: kinematic viscosity at 100° C., 5.2 mm²/s; viscosityindex, 140; sulphur content, not more than 10 ppm by mass](1-2) Base Oil B: Fischer-Tropsch derived base oil (XHVI 8.2)[Characteristics: kinematic viscosity at 100° C., 8.2 mm²/s; viscosityindex, 144; sulphur content, not more than 10 ppm by mass](1-3) Base Oil C: Co-oligomer of ethylene and α-olefins (Lucant HC40)[Characteristics: kinematic viscosity at 100° C., 40 mm²/s; viscosityindex, 155; sulphur content, not more than 10 ppm by mass]2. Zinc dithiophosphates(2-1) ZnDTP-1: Zinc dialkyldithiophosphate having secondary alkyl groupswith 3 to 6 carbons [Constituents (values for elemental analysis): Zn11.1% by mass, P 10.0% by mass, S 21% by mass](2-2) ZnDTP-2: Zinc dialkyldithiophosphate having secondary alkyl groupswith 4 to 6 carbons [Constituents (values for elemental analysis): Zn7.7% by mass, P 7.2% by mass, S 15% by mass]3. Ashless dispersants(3-1) Succinimide-1: Borated polybutenyl succinimide (mono)[Constituents (values for elemental analysis): N 2.2% by mass, B 1.96%by mass](3-2) Succinimide-2: Polybutenyl succinimide (bis) [Constituents (valuesfor elemental analysis): N 1.2% by mass](3-3) Succinimide-3: Borated polybutenyl succinimide (bis) [Constituents(values for elemental analysis): N 1.5% by mass, B 0.47% by mass]

4. Anti-oxidants

(4-1) Anti-oxidant-1: Amine-based anti-oxidant (Irganox L57)[Constituents: nitrogen content 4.5% by mass](4-2) Anti-oxidant-2: Hindered phenol-based anti-oxidant (Irganox L135)5. Metal deactivator: Benzotriazole derivative (Irgamet 39)6. Viscosity index improver: styrene-butadiene-based viscosity indeximprover7. Pour-point depressant: Polymethacrylate-based pour-point depressant8. Defoaming agent: Polydimethylsiloxane-based defoaming agent

Examples and Comparative Examples

The component materials were mixed in the proportions shown in Tables 1and 2, and lubricating oil compositions for use in diesel engine oilswere obtained. The proportions shown in Tables 1 and 2 are mass % unlessotherwise specified.

Tests

The following tests were carried out on Examples 1 to 4 and ComparativeExamples 1 to 6 in order to compare their characteristics.

(1) Parameter Calculation

Total value of [(amount of zinc in zinc dialkyldithiophosphate)×(amountof nitrogen in polybutenyl succinimide)] and [(amount of zinc in zincdialkyldithiophosphate)×(amount of nitrogen in amine-basedanti-oxidant)]

The amount of zinc and nitrogen described here are expressed with % bymass.

Evaluation criterion:

0.015 or more . . . Acceptable

Under 0.015 . . . Not acceptable

If this value is less than 0.015, the TGF will exceed 30% or the amountof cam nose wear will exceed 95 μm, which is not desirable. If it isbetween 0.015 and 0.06, both the TGF and the amount of cam nose wearwill be small, which means it is possible to achieve desirable results.If the value is more than 0.06, it is not favourable in terms ofeconomic efficiency.

(2) Detergency Test Based on TGF Value (TGF Value Measured after NissanTD25 Engine Test)

A test to evaluate piston detergency was carried out on the basis of theengine test procedure according to JASO M336:1998, which is adiesel-engine piston detergency test adopted also for JASO M355(Automotive Diesel Engine Oil Standard).

Evaluation criterion:

30% or less . . . Acceptable

Over 30% . . . Not acceptable

(3) Valve-Train Wear Tests

Valve-train wear tests were carried out in accordance with JASOM354:1999 (using Mitsubishi 4D34T4 engine).

Evaluation criterion:

Wear on cam nose 95 μm or less . . . Acceptable

Over 95 μm . . . Not acceptable

The cam nose wear value limit is based on the pass criteria for JASO'sDH-2.

In the case of the cam nose wear values used here, investigations werecarried out using the actual measured values themselves and noconversions of any kind were carried out.

Test Results

The test results for Examples 1 to 4 and Comparative Examples 1 to 6 aregiven in Tables 1 and 2.

Discussion

Example 1 did not contain any metallic detergent. The succinimide-3ashless dispersant gave a nitrogen amount of 0.15% by mass, theamine-based anti-oxidant gave a nitrogen amount of 0.08% by mass, andthe succinimide-based dispersant gave a boron amount of 0.047% by mass,whilst the ZnDTP gave a Zn amount of 0.10% by mass, so that theparameter for zinc amount×(succinimide nitrogen amount+amine-basedanti-oxidant nitrogen amount) had a value of 0.023, and the TGF was 12%and the cam nose wear was 7 μm. Furthermore, the sulphated ash was 0.23%by mass, meeting the criterion, so that satisfactory performance hadbeen obtained.

Example 2 did not use a metallic detergent. The main points were thatthe total nitrogen amount of the mixture of succinimide-1, succinimide-2and succinimide-3 gave a total nitrogen amount of 0.12% by mass, and theparameter value was therefore 0.020. The TGF was 12%, and the cam nosewear was 18 μm, which meant satisfactory performance had been achieved.

In the case of Example 3, the nitrogen amount of the succinimides was0.15% by mass, and it was a mixture of succinimide-1 and succinimide-2.The Zn amount was 0.1% by mass, and the amine-based anti-oxidant gave anitrogen amount of 0.0396% by mass, which meant that the parameter valuewas 0.019. The TGF value was 9% and the cam nose wear was 24.7 μm.

When the amine-based anti-oxidant nitrogen amount was 0.022% by mass, asin Example 4, the parameter value was 0.015, the TGF was 7% and the camnose wear was 84.9 μm, but this was within the range of satisfactoryperformance.

On the other hand, in the case of Comparative Example 1, thesuccinimide-based dispersant gave a nitrogen amount of 0.075% by mass.Also, the Zn amount was 0.077% by mass, and no amine-based anti-oxidantwas added, so that the parameter value was considerably reduced at0.006, the TGF value was 47%, and there was a substantial increase incam nose wear. In Comparative Example 2, the nitrogen amount from thesuccinimide-based dispersant was 0.12% by mass, and the nitrogen amountfrom the amine-based anti-oxidant was 0.08% by mass, whilst the Znamount was 0.05% by mass. This meant the parameter value was outside therange at 0.010, and the TGF was 39% but the cam nose wear exceeded 95 μmat 217 μm.

Comparative Example 3 gave a Zn amount of 0.05% by mass, a succinimidenitrogen amount of 0.10% by mass, an amine-based anti-oxidant nitrogenamount of 0.0792% by mass, and a parameter value of 0.009, which wasoutside the range. The TGF value was 55 and the valve-train weardeteriorated further to 300 μm. In the case of Comparative Example 4,where the Zn amount was 0.06% by mass, the succinimide nitrogen amountwas 0.15% by mass, and the amine-based anti-oxidant nitrogen amount was0.0396% by mass, the parameter value was 0.011, the TGF was 14% and thecam nose wear exceeded 95 μm at 130.7 μm.

In Comparative Example 5, where the Zn amount was 0.07% by mass and thesuccinimide nitrogen amount was 0.12% by mass, the parameter value was0.011, and the TGF was satisfactory at 24%, but the cam nose wearincreased substantially to give 235.6 μm. In Comparative Example 6, theamount of succinimide-3 was made the same as in Example 1, and the Znamount was 0.07% by mass, whilst the amine-based anti-oxidant nitrogenamount was 0.0396% by mass, which meant the parameter value was 0.013,the TGF was 11% and the cam nose wear was 99 μm, slightly exceeding thecamshaft wear limit of 95 μm.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Constituent Base Oil A 16.5 16.1 35 36.3Base Oil B 65.6 68.4 36.8 36.2 Base Oil C 14 14 ZnDTP-1 0.9 0.9 ZnDTP-21.3 1.15 Succinimide-1 1.2 2.4 Succinimide-2 1.6 8.1 Succinimide-3 10 510 Anti-oxidant-1 1.8 1.8 0.9 0.5 Anti-oxidant-2 0.5 0.5 1.5 1.5 Metaldeactivator 0.2 0.1 0.05 Viscosity index 4 4 improver Pour-point 0.3 0.30.3 0.3 depressant Defoaming agent 10 ppm 0.02 ppm 0.03 ppm 0.03 ppmElemental analysis (mass %) Ca 0 0 0 0 Zn 0.1001 0.0999 0.0999 0.08855 P0.0936 0.09 0.09 0.0828 S 0.195 0.20151 0.20151 0.1725 N in succinimides0.15 0.1206 0.15 0.15 N in anti-oxidant 0.0792 0.0792 0.0396 0.022 S inbase oil 0 0 0 0 B in succinimides 0.047 0.047 0.047 0.047 Sulphated ash0.23 0.22 0.22 0.22 Test results Parameter 0.023 0.020 0.019 0.015calculation Detergency (TGF) % 12 25 9 7 Valve-train wear 7.0 18.0 24.784.9 μm

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Ex. 6 Constituent Base Oil A 37.8 16.1 16 16 36.53 16 Base Oil B 40.3569.05 69.55 66.32 38 66.28 Base Oil C 14 14 ZnDTP-1 0.45 ZnDTP-2 1 0.650.78 0.92 0.92 Succinimide-1 1.2 1.2 1.2 Succinimide-2 1.6 1.6Succinimide-3 5 5 5 10 5 10 Anti-oxidant-1 1.8 1.8 0.9 0.9 0.9Anti-oxidant-2 1.5 0.5 1.5 1.5 1.5 1.5 Metal deactivator 0.05 0.2 0.050.1 Viscosity index improver 4 4 4 4 Pour-point depressant 0.3 0.3 0.30.3 0.3 0.3 Defoaming agent 0.03 ppm 10 ppm 0.02 ppm 0.03 ppm 0.03 ppm0.03 ppm Elemental analysis (mass %) Ca 0 0 0 0 0 0 Zn 0.077 0.049950.05005 0.06006 0.07084 0.07084 P 0.072 0.045 0.0468 0.05616 0.066240.06624 S 0.15 0.10075 0.0975 0.117 0.138 0.138 N in succinimides 0.0750.1206 0.1014 0.15 0.1206 0.15 N in anti-oxidant 0 0.0792 0.0792 0.03960.0396 0.0396 S in base oil 0 0 0 0 0 0 B in succinimides 0.0235 0.0470.047 0.047 0.047 0.047 Sulphated ash 0.21 0.19 0.19 0.20 0.02 0.20 Testresults Parameter calculation 0.006 0.010 0.009 0.011 0.011 0.013Detergency (TGF) % 47 39 55 14 24 11 Valve-train wear μm 478.6 217.4300.8 130.7 235.6 99.1

1. A lubricating oil composition for use in diesel engines whichcomprises, in the base oil, not more than 0.3% by mass of sulphated ash,from 0.01 to 0.2% by mass of nitrogen in succinimides, from 0.05 to0.12% by mass of zinc in zinc dithiophosphates, from 0.02 to 0.3% bymass of nitrogen in amine-based anti-oxidants, and from 0.01 to 0.08% bymass of boron, which further has a total value of [(zinc amount in zincdithiophosphates)×(nitrogen amount in succinimides)] and [(zinc amountin zinc dithiophosphates)×(nitrogen amount in amine-basedanti-oxidants)] in an amount of not less than 0.015, and which does notcontain salicylate, phenate or sulphonate metallic detergents.
 2. Thelubricating oil composition according to claim 1 wherein the base oil isa single base oil or a mixture selected from Group II, Group III, GroupIV and Group V, and where the sulphur component of the base oil is notmore than 50 ppm.
 3. The lubricating oil composition according to claim1 having a Top Groove fill according to Japanese Automobile StandardsOrganization M336:1998 Detergency Test Procedure of not more than 30%,and cam nose wear according to Japanese Automobile StandardsOrganization M354:1999 Valve-train Wear Test Procedure of not more than95 μm.
 4. The lubricating oil composition according to claim 1, whereinthe base oil contains secondary alkyl zinc dithiophosphates, wherein thealkyl groups have from 3 to 12 carbon atoms.